You don't mention the monitor you are using, but it's most likely a LCD Flatpanel. Those have usually much stricter timing requirements on digital inputs then on the analog inputs. Many will only sync at exactly 60Hz.

You may want to look into the XFree86.0.log file to see if the monitor reported the correct parameters via EDID/DDC. Look especially for a section "Supported additional Video Mode:" which is normally the optimal mode to run the monitor.

The braindead Philips 170B (which I have) reports the capabilities of the analog input on it's DVI-D connector, so autoconfiguration is guaranteed to be always wrong.

BTW - I forgot to mention one observation that
I though interesting. When the machine is
powered on I immediately get the out of range
(74.3k, 59.0) message from the monitor. When
X is started, the signal goes off momentarily (it
is doing something) and then the same message
comes back on the monitor. That sounds like
it is not setting the rates at all -- which
have been wrong since power on.